Investigation of Mexiletine Hydrochloride Binding on Transition Metal Oxide Nanoparticles by Capillary Electrophoresis

Author(s): Eman T. Elmorsi and Edward P.C. Lai

The binding affinity of pharmaceutically active compounds (PACs) onto transition metal oxide nanoparticles (TMONPs) is a physicochemical parameter that dictates their environmental bioavailability. Capillary electrophoresis (CE) was used successfully to determine the binding affinity of mexiletine hydrochloride (MEX.HCl) onto TiO₂, Co₃O₄, or ZnO nanoparticles individually in alkaline, neutral, and acidic aqueous suspension. The binding process was modeled using linear/nonlinear kinetics and Langmuir/Freundlich adsorption isotherms. Interestingly, TiO₂ nanoparticles demonstrated the highest binding affinity of 81(±1) % at pH 9.4 for MEX.HCl in the concentration range from 15 to 75 μg/mL. The maximum binding capacity (q_max) values for TiO₂, Co₃O₄, and ZnO at pH 9.4 were 27.0, 26.4, and 25.2(±1) mg/g, respectively. MEX.HCl molecules moved inside the porous TMONPs with a binding rate ranking of linear pseudo-second order > non-linear pseudo-second order > linear pseudo-first order > non-linear pseudo-first order. The binding isotherm favors the linear Freundlich > linear Langmuir > nonlinear Freundlich > nonlinear Langmuir models. Overall, MEX.HCl binds onto heterogeneous TMONP surfaces via electrostatic interactions and coordination bonds.